You have to define what you mean by mil-spec if youre gonna go down that road.
When a company (other than Colt) says "mil-spec" on their buffer tubes, theyre really only referring to OD.
Not even BCMs tubes are true "mil-spec."
TRUE mil spec tubes are forged 7075 (or perhaps impact extruded?), with rolled threads, straight back, with drain hole, 4 position, hard coat anodized, with dry film lube applied.
Few tubes are made that way, so the industry genrally accepts the term "mil-spec" as applied to buffer tubes to simply refer to outside diameter of the portion of the tube the buttstock fits on.
EDIT TO ADD- I just took one of my BCM lowers out of the safe, because curious. It has rolled threads, but it appears to have been turned on a lathe, has a slight ridge. Doesn't matter, don't care.
Your tube is not Mil-Spec, but your tube is fine. Go shoot your gun and don't worry about it.
Last edited by BFS; 10-22-17 at 15:29. Reason: Add info
How could you tell the threads were rolled or cut?
Not sure if it’s 100%, but if they are tube OD they I assume they are cut. If the threads OD are greater than tube OD, I assume they are rolled on. The end of the thread where it stops and goes to the tube is different as well.
Hopefully someone with more technical knowledge chime in.
If you have two to compare it's obvious. Sometimes you can tell on the last few threads if it is rolled as the top of the thread will be "M" shaped. Unfortunately, since this looks sloppy, most quality places turn the last five or six threads flat. Also, if the thread ends suddenly - it's cut. Rolled threads usually fade out over a quarter turn or more.
But honestly, most places that make mil-spec diameter extension roll the threads in, its easier than cutting them, even the "mil-spec" UTG extensions have rolled threads.
If you are really worried about such things, just buy from a well known and respected seller....
Last edited by lysander; 10-23-17 at 18:10.
And the ones I've seen up close and in person look rolled. Just because they machined the last few threads to clean them up and put a slight step in it doesn't mean the threads aren't rolled . . . (see below)
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